Electronic assemblies having components with edge connectors

ABSTRACT

Circuit assemblies can be electrically interconnected by providing a circuit assembly having a top surface, a bottom surface, and a perimeter edge connecting the top and bottom surfaces, the perimeter edge being formed of insulative material and having a plurality of conductive features embedded in and exposed on the surface of the edge. The conductive features are arranged in contact sets, and each contact set is separated from adjacent contact sets by a portion of the perimeter edge that is free of conductive features. Each contact set includes conductive features that together form a distributed electrical connection to a single node. The insulative material is selectively removed to form recesses adjacent the conductive features exposing additional surface contact areas along lateral portions of the conductive features in the recesses.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 15/941,068, filed on Mar. 30, 2018, which is a divisionalapplication of U.S. patent application Ser. No. 14/596,914, filed onJan. 14, 2015, which is related to U.S. patent application Ser. No.14/596,848 titled “Isolator with Integral Transformer,” filed on Jan.14, 2015, now U.S. Pat. No. 9,508,485, issued on Nov. 29, 2016, and U.S.patent application Ser. No. 14/596,914 titled “Power Adapter Packaging,”filed on Jan. 14, 2015. The above applications are incorporated hereinby reference.

FIELD OF THE INVENTION

This invention relates to the field of encapsulating electronicassemblies and more particularly to encapsulated power converters andother electronic assemblies that have components with edge connectors.

BACKGROUND

Contemporary electronic power systems require power converters capableof deployment at the point of load. Competing considerations requireincreasing power density, decreasing mounting area on customermotherboard, and lower cost.

An encapsulated electronic module, such as an electronic power convertermodule for example, may comprise a printed circuit assembly over-moldedwith an encapsulant to form some or all of the package and exteriorstructure or surfaces of the module. Encapsulation in this manner mayaid in conducting heat out of the over-molded components, i.e.,components that are mounted on the printed circuit assembly and coveredwith encapsulant. In the case of an electronic power converter module,the printed circuit assembly may include one or more inductivecomponents, such as inductors and transformers. Encapsulated electronicpower converters capable of being surface mount soldered to a customermotherboard are described in Vinciarelli et al., Power Converter Packageand Thermal Management, U.S. Pat. No. 7,361,844, issued Apr. 22, 2008,(the “SAC Package Patent”) (assigned to VLT, Inc. of Sunnyvale, Calif.,the entire disclosure of which is incorporated herein by reference).Encapsulated electronic modules having at least one surface of amagnetic core structure exposed and methods for manufacturing the sameare described in Vinciarelli et al., Encapsulation Method and Apparatusfor Electronic Modules, U.S. patent application Ser. No. 12/493,773,filed Jun. 29, 2009, (the “Exposed Core Application”) (assigned to VIChip Inc. of Andover, Mass., the entire disclosure of which isincorporated herein by reference).

Methods of over-molding both sides of a printed circuit board assemblywhile leaving opposing regions on both sides of the printed circuitboard free of encapsulant are described in Saxelby, et al., CircuitEncapsulation Process, U.S. Pat. No. 5,728,600, issued Mar. 17, 1998 andSaxelby, et al., Circuit Encapsulation, U.S. Pat. No. 6,403,009, issuedJun. 11, 2002 (collectively the “Molding Patents”) (both assigned toVLT, Inc. of Sunnyvale, Calif. and incorporated by reference in theirentirety).

Leads for connecting the encapsulated power converter substrate to thecustomer motherboard are described in Vinciarelli et al., SurfaceMounting A Power Converter, U.S. Pat. No. 6,940,013, issued Sep. 6, 2005(the “J-Lead Patent”) (assigned to VLT, Inc. of Sunnyvale, Calif., theentire disclosure of which is incorporated herein by reference).

SUMMARY

In general, in one aspect, a method of electrically interconnectingcircuit assemblies is provided. The method includes providing a circuitassembly having a top surface, a bottom surface, and a perimeter edgeconnecting the top and bottom surfaces, the perimeter edge being formedof insulative material and having a plurality of conductive featuresembedded in the surface of the perimeter edge, the conductive featureseach including an exposed edge, the exposed edges being arranged intoone or more contact sets. Each contact set provides an electricalconnection to a respective electrical node of the circuit assembly,including one or more of the conductive features, being separated fromadjacent contact sets by a portion of the perimeter edge that is free ofconductive features, and being located at an elevation in the perimetersurface between the bottom surface and the top surface. The methodincludes selectively removing portions of the insulative material fromthe surface of the perimeter edge adjacent to selected ones of theexposed edges of selected ones of the conductive features exposingadditional surface area of the selected ones of the conductive features.The additional surface area is recessed from the perimeter edge andtogether with the adjacent exposed edge forms a three dimensionalcontact.

Implementations of the method may include one or more of the followingfeatures. The additional surface area can form an angle greater than 45degrees to the perimeter edge. The method can include preparing theadditional surface area of the conductive features for solder wetting.The method can include applying solder paste to the exposed portions ofthe conductive features. The method can include wetting the conductivefeatures in the recesses and along the perimeter surface with solder.The method can include placing an external conductive terminal adjacentthe conductive features and forming a solder connection between theexternal conductive terminal and the conductive features. The method caninclude forming a solder connection between each set of the conductivefeatures and a respective conductive pad on a printed circuit board. Themethod can include forming a solder connection between each set of theconductive features and a respective terminal of a lead frame.

In general, in another aspect, a method of forming an electricalconnection to an electronic module is provided. The method includesassembling a panel including a substrate and having one or moreconductive features enclosed within the panel and unexposed to anexterior surface of the panel, the one or more conductive features eachbeing electrically connected to a respective electrical node of thepanel and being located along a cut line; cutting the panel along thecut line exposing a contact edge of each of the one or more conductivefeatures, wherein each contact edge is embedded in and forms part of aperimeter surface of the electronic module after the cutting; andselectively removing portions of material from the perimeter surfaceadjacent to selected ones of the contact edges of selected ones of theconductive features exposing additional portions of the selected ones ofthe conductive features. The additional portions are recessed from theperimeter edge and together with the adjacent exposed edge forms a threedimensional contact.

Implementations of the method may include one or more of the followingfeatures. The method can include preparing the contact edges and theadditional portions of the conductive feature for solder wetting. Themethod can include wetting the contact edges and the additional portionsof the conductive features with solder. The method can include forming ametallic bond between the contact edges and the additional portions andan external conductive terminal. The method can include forming ametallic bond between the contact edges and the additional portions ofthe conductive features and a conductive pad on a printed circuit board.The method can include forming a solder connection between the contactedges and the additional portions of the conductive features and aterminal of a lead frame.

In general, in another aspect, an apparatus includes a circuit assemblyhaving a modular package including a first surface, a second surface,and a perimeter edge connecting the first and second surfaces, theperimeter edge being formed of insulative material and having one ormore conductive features embedded in the surface of the perimeter edge.The conductive features each has a contact edge generally coplanar withthe perimeter edge and one or more additional surfaces extending fromthe contact edge into a respective recess in the insulative material,the recess being open to the perimeter edge wherein the contact edge andthe additional surface together form a three dimensional contact.

Implementations of the apparatus may include one or more of thefollowing features. The three dimensional contacts are arranged in aplurality of contact sets, each contact set having a plurality of threedimensional contacts, each contact set being separated from adjacentcontact sets by a portion of the perimeter edge that is free ofconductive features, the plurality of three dimensional contacts of eachcontact set together form a distributed electrical connection to asingle electrical node in the circuit assembly. The perimeter edge caninclude an edge of a printed circuit board (“PCB”), the PCB having aplurality of conductive layers, and the conductive features compriseselected portions of the conductive layers and are located at anelevation in the perimeter surface between the first surface and thesecond surface. The recesses can be formed in insulation layers in thePCB. Each contact set can be separated from adjacent contact sets by aportion of the perimeter edge that is free of conductive features, inwhich a first distance between two adjacent contact sets is at leasttwice as large as a second distance between two adjacent conductivefeatures, the first and second distances being measured along adirection substantially perpendicular to the top surface. Each contactset can be separated from adjacent contact sets by a portion of theperimeter edge that is free of conductive features, in which a firstdistance between two adjacent contact sets is at least five times aslarge as a second distance between two adjacent conductive features, thefirst and second distances being measured along a directionsubstantially perpendicular to the top surface. The apparatus caninclude an external conductive terminal electrically coupled to aselected contact set. The apparatus can include an external circuitboard having a plurality of conductive pads, and a solder connectionbetween each conductive pad and a respective contact set. The apparatuscan include a lead frame having a plurality of terminals, and a solderconnection between each terminal and a respective contact set.

In general, in another aspect, an apparatus includes a circuit boardhaving a plurality of conductive layers embedded in an insulativematerial, in which two or more of the embedded conductive layersprotrude from, an edge, or a recess in the edge, of the circuit board,each protruded portion of the conductive layer having an exposed surfacecontact area. Some of the protruded portions of the conductive layersare arranged in a contact set, each protruded portion of the conductivelayer is separated from adjacent protruded portions of the conductivelayers by a portion of the external edge that is free of conductivefeatures, the protruded portions of the conductive layers of the contactset together form a distributed electrical connection to a single node.

Implementations of the apparatus may include one or more of thefollowing features. The protruded portions of the conductive layers canbe arranged in a plurality of contact sets, each contact set having aplurality of conductive protruded portions in which each conductiveprotruded portion is separated from adjacent conductive protrudedportion by a portion of the external edge that is free of conductivefeatures, the plurality of conductive protruded portions of each contactset together form a distributed electrical connection to a single node.Each contact set can be separated from adjacent contact sets by aportion of the perimeter edge that is free of conductive features, inwhich a first distance between two adjacent contact sets is at leasttwice as large as a second distance between two adjacent conductivefeatures, the first and second distances being measured in a thicknessdirection of the circuit board. The apparatus can include two externalconductive terminals that are electrically coupled to two respectivecontact sets that are aligned and spaced apart in the thicknessdirection. The apparatus can include an external circuit board having aplurality of conductive pads, and a solder connection between eachconductive pad and a respective contact set. The apparatus can include alead frame having a plurality of terminals, and a solder connectionbetween each terminal and a respective contact set. The apparatus caninclude an external conductive terminal that is electrically coupled tothe exposed conductive protruded portions of the contact set. Theapparatus can include a second circuit board having a conductive padthat is electrically coupled to the exposed conductive protrudedportions of the contact set.

In general, in another aspect, an apparatus includes a circuit assemblyhaving a modular package including a multilayer printed circuit boardthat has an insulative material and one or more conductive layersembedded in the insulative material, in which the one or more conductivelayers partially protrude from an edge surface of the insulativematerial to form one or more three-dimensional contacts, eachthree-dimensional contact has a thickness that is substantially the sameas the thickness of the corresponding conducive layer and has a widththat is greater than the thickness.

Implementations of the apparatus may include one or more of thefollowing features. The three dimensional contacts can be arranged in aplurality of contact sets, each contact set having a plurality of threedimensional contacts, each contact set being separated from adjacentcontact sets by a portion of the edge of insulative material that isfree of conductive features, the plurality of three dimensional contactsof each contact set together form a distributed electrical connection toa single electrical node in the circuit assembly. Each contact set canbe separated from adjacent contact sets by a portion of the edge of theinsulative material that is free of conductive features, in which afirst distance between two adjacent contact sets is at least twice aslarge as a second distance between two adjacent three dimensionalcontacts, the first and second distances being measured along athickness direction of the printed circuit board. Each contact set canbe separated from adjacent contact sets by a portion of the edge of theinsulative material that is free of conductive features, in which afirst distance between two adjacent contact sets is at least five timesas large as a second distance between two adjacent three dimensionalcontacts, the first and second distances being measured along athickness direction of the printed circuit board. The apparatus caninclude an external conductive terminal electrically coupled to aselected contact set. The apparatus can include an external circuitboard having a plurality of conductive pads, and a solder connectionbetween each conductive pad and a respective contact set. The apparatuscan include a lead frame having a plurality of terminals, and a solderconnection between each terminal and a respective contact set.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an electronic module 100.

FIG. 2 shows a panel assembly 120 comprising a plurality of electronicmodules before singulation.

FIG. 3 shows an exploded view of the panel assembly revealing the heatsink panels 121 and 122 and internal PCB panel 124.

FIG. 4 shows the panel assembly 120 with the top heat sink panel 121removed.

FIG. 4A shows an exploded view of the PCB panel and lower heat sinkpanel in a modified panel assembly 120.

FIG. 4B shows a cross-section of the panel assembly 120A along lines4B-4B in FIG. 4A.

FIG. 5 shows a plan view of the PCB panel 124 assembled with the bottomheat sink panel 122.

FIG. 6 shows a cross-section of the panel assembly 120.

FIG. 7 shows a partial cross section of the panel assembly closed in amold.

FIG. 8 shows another partial cross section of the panel assembly closedin a mold.

FIG. 9A shows a plan view of the panel assembly 120 followingsingulation.

FIGS. 9B, 9C show optional channels formed in the panel beforesingulation.

FIGS. 10A, 10B show single modules 115, 115B after singulation.

FIG. 11 shows an enlarged portion of the module 115 revealing details ofexposed buried-embedded interconnects.

FIG. 12 shows a cross section of the singulated module 115 of FIG. 10A.

FIG. 13 shows a connector assembly.

FIG. 14 shows an exploded view of the connector assembly.

FIG. 15 shows a horizontal through-hole mount module 200.

FIG. 16 shows an exploded view of the through-hole mount module 200.

FIG. 17 shows a horizontal surface-mount module 300.

FIG. 18 shows an exploded view of the surface-mount module 300.

FIG. 19 shows an alternative horizontal surface-mount module 400.

FIG. 20 shows a top view of the surface-mount module 400.

FIG. 21 shows an exploded top view of module-connector set 500.

FIG. 22 shows an exploded view of the connector set 503.

FIG. 23 shows an exploded bottom view of module-connector set 500.

FIG. 24 shows an isometric view of the module-connector set 500assembled.

FIG. 25 shows an alternative horizontal through-hole flush-mount module600 exploded from a customer PCB.

FIG. 25A shows an alternative horizontal through-hole flush-mount module650 exploded from a customer PCB.

FIG. 26 shows the horizontal through-hole flush-mount module 600assembled onto a customer PCB.

FIG. 27 shows top and bottom plan views of a section of a PCBillustrating symmetry of component layouts.

FIG. 28 shows an exploded perspective view of a panel assembly 720including a manifold plate.

FIG. 29 is an exploded side view of the panel assembly 720 showing thePCB mated with the manifold plate.

FIG. 30 shows a top plan view of the panel assembly 720.

FIG. 31 shows a top plan view of the panel assembly 720 with the topheat sink panel removed.

FIG. 32 shows a side view of the panel assembly 720 closed in a mold.

FIG. 33 shows a top perspective view of a singulated module.

FIG. 34 shows a bottom perspective view of a singulated module.

FIG. 35 shows a top exploded perspective view of a singulated module andconnectors.

FIG. 36 shows a bottom exploded perspective view of a singulated moduleand connectors.

FIG. 37 shows an exploded perspective view of a PCB panel assemblyincluding a manifold plate.

FIG. 38 is an exploded side view of the PCB panel assembly with the PCBmated with the manifold plate.

FIG. 39 shows a top plan view of the PCB panel assembly.

FIG. 40 shows a side view of the PCB panel assembly closed in a mold.

FIG. 41 shows a top plan view of the encapsulated PCB panel assembly andmanifold plate.

FIG. 42 shows a cross-sectional view of the encapsulated panel assembly.

FIG. 43 shows a bottom (as molded) isometric view of an encapsulated PCBpanel.

FIG. 44 shows a top (as molded) isometric view of an encapsulated PCBpanel.

FIG. 45 shows a side view of a PCB panel.

FIG. 46 shows a side view of the PCB panel of FIG. 45 with exposed edgeconnectors.

FIG. 47 shows the PCB panel connected to an external circuit board.

FIGS. 48A and 48B show perspective views of PCB panels having split barcodes.

FIG. 49 shows the PCB panel of FIG. 48B in which the bar codes areconnected to conductive terminals for surface mounting.

FIG. 50 shows the PCB panel of FIG. 48B in which the bar codes areconnected to a lead set for through hole mounting.

Like references symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

I. Vertical PCB Package.

Referring to FIG. 1, an electronic module 100, e.g., a power converter,is shown having a generally rectangular form factor with two large faces114A, 114B covered by heat sinks 101, 102. As shown between the heatsinks 101 and 102, the module 100 includes a printed circuit board(“PCB”) 104 having its large faces arranged generally coplanar to thetwo large faces 114A, 114B of the electronic module 100. Electroniccomponents (FIGS. 3, 5, 6) may be mounted to one or both sides of thePCB 104 and electrically interconnected, e.g. by conductive traces on orin the PCB 104 to form the module circuitry. Using a power converter asan example, the electronic components may include power transistors,control ICs, and discrete resistors and capacitors. One or more magneticcore structures may be provided, which in combination with conductivetraces on PCB 104, may form planar magnetic components such as inductorsand transformers.

The electronic components may protrude from one or both sides of the PCB104 to varying degrees depending upon component size. Spaces between thefaces of PCB 104 and the components on the PCB on one hand and theinterior surfaces of the heat sinks on the other hand may be filled withmolding compound, which when cured may form integral structural layers105, 106 as shown in FIG. 1 and further provides a thermally conductivemedium in which heat may be readily conducted away from the PCB andcomponents to the heat sinks 101, 102. The interior surfaces of the heatsinks may be contoured to match the height of one or more of thecomponents while maintaining an appropriate clearance for insulation andsafety agency requirements. Contouring the heat sinks 101, 102 in thisway: (1) to match the height of the magnetic core structure may be usedas an alternate approach to the exposed core encapsulation methoddescribed in Vinciarelli, Encapsulation Method and Apparatus forElectronic Modules, U.S. patent application Ser. No. 12/493,773 filedJun. 29, 2009 (assigned to VI Chip Corp. of Andover, Mass., the entiredisclosure of which is incorporated herein by reference); (2) to matchthe height of lower profile components, such as power semiconductors,may (a) increase thermal performance in the case of heat dissipatingcomponents by replacing molding compound with heat sink metal; and (b)reduce cost generally by reducing the volume of molding compoundrequired; and (c) further reduce cost by allowing less expensive moldingcompound to be used because of reduced thermal pathways through theencapsulant, easing the thermal conductivity requirements of theencapsulant (e.g., an encapsulant having a 1 degree Celsius per wattthermal resistance may be used with the contoured heat sink instead ofan encapsulant having a 3 degrees Celsius per watt thermal resistanceused without the contoured heat sink).

A connector 103, including terminals 108, 109, 110 and standoffs 107,may be provided as shown along an edge of the PCB 104 to make electricalconnections between the electronic module 100 and external circuitry. Asshown in FIG. 1 with the connector 103 situated along one edge of themodule 100, preferably one of the longest edges, the module 100 may bemounted vertically, i.e. with its internal PCB 104 perpendicular to achassis or another circuit board such as a motherboard. Using thevertical mount module construction illustrated in FIG. 1 for a powerconverter may provide advantages over the more conventional horizontalmounting technique. For example, using the vertical PCB arrangement mayallow use of a magnetic core structure that is thicker than in ahorizontal PCB configuration, e.g. because of height restrictions,enabling increased power throughput, as compared to a similar converterusing a horizontal PCB orientation. The length of the magnetic path maybe also reduced in the vertical PCB configuration further reducinglosses in the magnetic components. Shorter windings may also be usedfurther reducing transformer or inductor losses. Further details andvariations of, and a process for making, the electronic module will bediscussed below in connection with a panel molding process.

II. Panel Molding Process Integrated Mold

A. Overview

The electronic module 100 shown in FIG. 1 may be fabricated using apanel molding process described with reference to FIGS. 2-9. The panelmolding process may be used to produce a multiplicity of modules at atime. A PCB panel 124 may be provided with a plurality of individualcircuits for building the electronic modules. FIGS. 3, 4, and 5 show thePCB panel 124 populated with electronic components revealing a 3-by-4pattern of twelve circuits to make twelve individual modules 115(labeled 115A through 115L in FIG. 5). The illustrative example of FIGS.3-5, being for power converters, includes magnetic core structures 131(FIG. 3) in addition to electronic components 132. As shown in FIG. 5,the pattern of individual circuits 115A-115L are arranged close togetherand separated by small spaces 135 preferably sufficient to allow the PCBpanel to be cut during the singulation process without necessitating twocuts between modules or unnecessary waste of PCB material. The spacingmay be adjusted based upon the cut dimensions produced by the equipmentused to make the cuts.

The PCB panel 124 containing the multiplicity of the electronic circuits(115A-115L in FIG. 5) may be assembled with matching heat sink panels121, 122 as shown in FIG. 3 to form a panel assembly 120 (FIG. 2). Asshown in FIGS. 3 and 6, the two heat sink panels 121 and 122 whenassembled together may form an internal cavity 146, which completelyencloses the populated PCB panel 124. FIGS. 2 and 6 show that the heatsink panels 121 and 122 may be pressed together (e.g. by a mold press161, 162 as shown in FIG. 7) to form a seal 123 (FIGS. 2, 6-8) aroundthe perimeter of the internal cavity 146. In this example, the heat sinkpanels 121 and 122 also function as mold panels by forming a mold cavity(e.g., the internal cavity 146) that may be filled at least in part byan encapsulant encapsulating the surfaces of the PCB panel 124 and theelectronic components on the PCB panel 124.

B. Heat Sink Panels

Referring to FIG. 2, the heat sink panels 121, 122 may include fins onthe exterior surfaces as shown. The fins may be arranged in anydirection relative to the panel or in any pattern and may vary inheight, thickness, and spacing as required for the particularapplication. For example, modules 115 and 115B shown in FIGS. 10A and10B respectively illustrate longitudinal and transverse finorientations. Alternatively, one or both of the heat sink panels mayhave a generally flat exterior surface omitting the fins altogether. Forexample, FIGS. 17 and 25 show modules 315 and 615 produced when bothheat sink panel exterior surfaces are flat and one is flat and one isfinned, respectively. The thickness of the panels between the internalcavity and the external surface may be varied to suit the particularrequirements of the application.

C. Heat Sink Internal Contours

Referring to FIG. 3, the contoured interior surface of the bottom heatsink panel 122 is shown including a 3-by-4 repeating pattern of twelve(A through L) prominent recesses 141 and shallower recesses 142 and 143.Recesses 141 may be matched to the downward protruding portion ofmagnetic core structures 131. Similarly, recesses 142 and 143 may bematched to other downwardly protruding components on the PCB panel 124.Note that in the example of FIG. 3, because the core structure 131protrudes from the PCB 124 more than the other components, the recesses141 are deeper than recesses 142, 143. Although not visible in FIG. 3,the interior surface of heat sink panel 121 may similarly includecontour features to match the components and core structure on theupward facing side of the PCB panel 124 (e.g. as shown in thecross-section of FIGS. 6, 7). Although the interior contour of panel 122in FIG. 3 is shown including three recesses 141, 142, 143 repeated foreach circuit (A through L in the 3-by-4 pattern), the interior contoursof the heat sink panels 121 and 122 may range from simple flat surfaces(accommodating the height of the tallest component) to a complexarrangement of a multiplicity of recessed and protruding features(accommodating a multiplicity of component heights) which at the extremecould match every component individually.

Additional features may be provided in the heat sink panels tofacilitate the panel molding process, to enhance the mechanicalintegrity or performance of the finished module 100, or to satisfysafety agency clearance requirements for the finished product. By way ofexample undercut features, such as undercuts 148 shown in FIGS. 6, 7,and 12 may be provided at each circuit site (i.e. within each individualmodule location) in the heat sink panels 121, 122. As shown theundercuts 148 may be provided in selected recesses, such as recesses143-1 and 143-2, and may be dispersed along one or more of the boundarylines of each circuit 115. During encapsulation, molding compound fillsthe recesses and trenches and their respective undercuts 148. Whencured, the hardened molding compound in the undercuts forms adovetail-like joint securing the heat sinks to the encapsulated PCB 124.When provided at each circuit site, the undercuts secure the heat sinks101, 102 to the PCB 104 in the individual module 115 providingmechanical integrity after singulation. Referring to the cross-sectionof a singulated module 115 in FIG. 12, dovetail interfaces 149-2 and149-1 are shown securing the top and bottom heat sinks 101, 102 to theencapsulated PCB assembly.

Additionally, clearance features may be provided in the heat sink panelsto satisfy minimum safety agency clearances between electrical contactson the PCB 124 and the metal heat sinks 121, 122. As shown in FIGS. 6and 7, trenches 147 may be provided in heat sink panels 121 and 122along the side of each module 115 (the long side as shown in FIGS. 6 and7) where electrical contacts (discussed in more detail below) areexposed in or on the PCB 124. The trenches 147 may also include theundercut features 148 discussed above. For example, cut trench 147 inFIG. 12 results in a recess 150 of the heat sink 101 away from the edge104E of the PCB 104 after singulation.

D. PCB-Heat Sink Registration

Registration features may be provided in one or both of the heat sinkpanels 121, 122 helping to correctly position the PCB panel 124 in thecavity 146 relative to the heat sink panels 121, 122 (which isparticularly important when the panel is cut during the singulationprocess) and to correctly position the heat sink panels relative to eachother during assembly and during subsequent molding processes. Referringto FIGS. 3 and 4, beveled corners 144 may be provided in heat sink panel122 to interface with matching indentations 133 which may be provided inPCB panel 124 for registration when assembled together (FIGS. 4 and 5).FIG. 5, which is a top plan view of the PCB panel 124 assembled with thebottom heat sink 122, shows the beveled corners 144 interfacing with theindentations 133.

Referring to FIG. 4A, a modified version of the assembly is shown. Asshown, a registration pin 151 is press fit into a registration hole 152in the lower heat sink panel 122 and a matching registration hole 134 isprovided in the PCB panel 124. The completed panel assembly, includingthe lower heat sink panel 122, PCB panel 124, and upper heat sink panel121, is shown in FIG. 4B in cross-section taken along the broken lines4B-4B in FIG. 4A. As shown in FIG. 4B, the registration pin 151, whichfits snugly in registration holes 152 and 134, provides registration forthe PCB panel 124 relative to the lower heat sink panel 122. Anindentation 153 may be provided in the opposite heat sink panel (121) toaccommodate protrusion of the pin 151 past the PCB 124. As showngenerally at 154 in FIG. 4B, the heat sink panels may include additionalfeatures to provide registration between the top and bottom heat sinkpanels. Although a registration pin is shown at one corner of the panel122 in FIG. 4A, it will be appreciated that additional pins may be usedat other locations. For example, FIG. 4 shows two registration holes134, one on a corner and another in the middle of the opposite side ofthe PCB panel 124.

E. Encapsulation

FIG. 6 shows a cross-sectional view (through lines 6-6 in FIG. 5) of thepanel 120 through an opening 125 and a conduit 145 in the heat sinkpanels. The openings 125, which may be slot shaped as shown (FIGS. 2, 3,4, 5, 9), may be connected to the interior cavity 146 of the panelassembly 120 by conduits 145 for conveying molding compound or ventingduring the panel molding process. The openings may be formed in one ofthe heat sink panels, e.g. openings 125 in the top heat sink panel 121as shown in FIGS. 2, 3, 4, 5, and 9, or in both heat sink panels, e.g.openings 125B in the top and bottom heat sink panels 121, 122 as shownin FIGS. 6 and 7. Referring to FIG. 6, the conduits 145 may be formed byrecesses in the interior surfaces of heat sink panels 121 and 122,connecting the openings 125 to the interior cavity 146. The recessesforming the conduit 145 may be situated near the edge 124C of PCB panel124 to allow the molding compound to flow over both top 124A and bottom124B surfaces of the PCB 124.

FIG. 7 shows an enlarged cross-section of one end of the panel assembly120 closed between an upper mold press 161 and lower mold press 162taken through some of the smaller components, e.g. components 132-1,132-2, i.e. through lines 6-6 in FIG. 5. A channel 163 may be provided,e.g. between the upper mold press 161 and lower mold press 162 as shown,to interface with openings 125. Molding compound may be forced throughthe channel 163 under pressure after the panel assembly 120 is closed inthe mold presses 161, 162. The dashed line 167 with directional arrowsin FIGS. 7 and 8 illustrates the flow of molding compound through thechannel 163 into openings 125 through conduits 145 over the top 124A andbottom 124B surfaces of the PCB panel 124 during encapsulation. Themolding compound may be forced into the internal cavity 146 to fill allof the unoccupied spaces between the heat sinks 121, 122 and the PCBpanel 124.

FIG. 8 shows an enlarged cross-section of one end of the panel assembly120 closed between an upper mold press 161 and lower mold press 162taken through the magnetic core structures, i.e. through lines 8-8 inFIG. 5. Each magnetic core 131 is shown having an upper E-core 131-2 anda lower E-core 131-1 separated by a gap 131-3. The cores have openings131-4 to accommodate windings formed on the PCB 124. As shown, the lowercore 131-1 and upper core 131-2 are accommodated by recesses 141-1 and141-2 in the lower heat sink 122 and upper heat sink 121, respectively.As shown, compliant pads 136 may be provided on the surfaces of thecores 131-1 and 131-2 or in recesses 141-1, 141-2 to accommodatedimensional differences in the components. The compliant pads may bechosen for good thermal conduction and optionally adhesive propertiesfacilitating heat removal from the cores into the heat sink whileoptionally providing structural integrity to the assembly. Gap Pad A2000available from the Bergquist Company, 18930 West 78th St, Chanhassen,Minn. 55317 is one example of the type of compliant pad that may beused. Alternatively and perhaps depending upon the tolerances involved,a phase change material may accommodate the dimensional differenceduring assembly and when cured afterward provide structural integritybetween the heat sinks and the cores.

Molding compound may be deposited in one or more of the recesses, e.g.recesses 141-1 or 141-2, in the internal cavity prior to assembly of thePCB panel 124 into one or both of the heat sink panels 121, 122 toensure that the molding compound fills narrow spaces between the heatsink and the components, e.g. the cores 131-1, 131-2. One or more ventopenings (not shown) may be provided in the heat sink panels, preferablyat an end opposite the fill openings 125, to allow the molding compoundto flow completely through the internal cavity 146. The cavity may befilled with encapsulant either (1) by transfer through one or moreconduits, (2) by measured deposition of encapsulant during assembly ofthe panels, or (3) by both measured deposition during assembly andtransfer through conduits.

As shown in FIGS. 4, 5, and 6, the border areas between the modules andaround the periphery of the PCB panel 124 may be minimized to avoidwasted PCB material. Because the heat sink panels 121 and 122 closeagainst each other rather than the PCB panel 124, areas on the PCBnormally reserved for closing the mold may be eliminated furtherreducing PCB waste and thus overall cost.

After the panels are assembled together and the interior cavities arefilled with molding compound, the panel assembly 120 may be cured, e.g.by elevating the temperature.

F. Singulation

Singulation is the process by which individual modules, e.g. singulatedmodule 115 in FIG. 10A, are separated from the panel assembly 120, e.g.by cutting. The panel assembly 120 may be singulated after the moldingcompound is cured. The panel assembly 120 is separated from the upperand lower mold presses 161, 162 and may be cut, e.g. along lines 128,129 as shown in FIG. 9A, to singulate the modules 115A-115L. Forexample, a narrow saw may be used to cut through the layers (e.g. asshown in FIGS. 1, 10A, 10B, 12) of panel 120, which may include heatsink 101, cured molding compound 105, PCB 104, cured molding compound106, and heat sink panel 102. For example, a 0.025 inch thick saw suchas model number EAD-3350 available from Disco Corp., Ota-ku, Tokyo,Japan may be used. Referring to the cross-sectional views of FIGS. 6 and7, dashed lines 129 illustrate the lines along which the panel 120 maybe cut to singulate modules 115D, 115E, and 115F. As shown, the cuts 129(along the long side of the individual modules 115) go through themiddle of the trenches 147. The trenches 147 may be made wide enough andthe cuts 129 may be made at an appropriate distance from the edges ofthe trench 147 to ensure that a minimum thickness of cured moldingcompound remains in the trench after singulation to be mechanicallyrobust. The trenches 147 may also be used to reduce the thickness ofmetal through which the saw must cut during singulation, e.g. byoptionally providing trenches along the perimeter of each module.

G. Electrical Connections

Interconnection features may be embedded in the PCB panel 124,preferably along the boundaries of the individual circuits, so thatelectrical contacts are at least in part formed by or exposed duringsingulation. To maximize the area on a PCB panel 124 available forcircuitry, the interconnection features may preferably be buried in thePCB panel 124 below the top and bottom surface layers. For example, theinterconnection features may be formed in the inner conductive layersbut not occupying valuable area on the surface conductive layers,potentially reducing setback and other spacing requirements. Theinterconnect features therefore are preferably formed in the PCB panel124 before the panel 120 is assembled and exposed when the panels arecut, e.g. during singulation. The interconnection features may comprisea pattern of conductive layers or buried vias (frequently used to formconnections between internal conductive layers) or both in the PCBsituated along the circuit boundary, i.e. lying in the cut line, e.g.cut line 129 (FIG. 9A).

Referring to FIG. 10A, a module 115 is shown after singulation. Exposedinterconnects 111, 112, and 113 are shown embedded in the edge of thePCB 104 along one of the edges 116 of the module 115. As shown in FIG.10A, longer connections 111 and 113 provide greater interconnect surfacearea and higher current carrying capacity, making them amenable for useas power connections, than shorter connections 112 which have lessinterconnect area and lower current carrying capacity, making themuseful for control signal connections. FIG. 11 shows an enlarged view ofa portion of the module 115 along edge 116 revealing detail of the twointerconnections 111 after singulation. The width along the boundary andnumber of the conductive features arranged vertically through the PCBlayers may be adjusted to provide the requisite contact area for eachconnection. In the example of FIG. 11, conductive features, e.g.conductive lands 111A through 111L, formed along the cut line on aplurality of the conductive layers of the PCB form a stack of conductivestrips resembling a bar code after singulation. The stack of conductivelands may provide more contact area than possible with a single buriedvia. In FIG. 11, each interconnect 111 is made up of twelve lands, eachland being formed on a respective one of twelve inner conductive layers.Note that FIG. 11 shows the twelve lands (111A through 111L) buriedbelow the top 124A and bottom 124B surfaces of the PCB, i.e. notoccupying surface area on those layers. During singulation, the saw cutsthrough the buried embedded lands, exposing the edges of the remainingconductive material forming the interconnects 111A through 111L shown inFIG. 11. Note that the buried embedded lands may be shared between twoadjacent modules 115 on the panel 120, e.g. where the PCB patterns arelaid out in mirror image to each other, allowing the modules to be laidout on the PCB panel close to a singulation cut width apart. Also, theinterconnect features may be aligned along a single module boundary asshown or may occupy two or more boundaries of each individual module inthe panel. The exposed edges may then be used to form electricalconnections immediately after singulation, i.e. before the cutinterconnects oxidize or may be protected against oxidation, e.g. with aconformal coating, such as an organic solderability preservative(“OSP”), applied after singulation, to ensure subsequent ability to formelectrical connections to the edges. For example, Entek Plus HTavailable from Enthone, Inc., a Division of Cookson Electronics, WestHaven, Conn. 06516 may be used as an OSP to protect the interconnects.

The number of lands, i.e. conductive layers, used to form eachinterconnect may be increased for better electrical connections orreduced for less critical connections. Although embedded conductivelands are shown in the example of FIGS. 10A, 11, additional oralternative conductive features may be used to form the interconnects.For example, buried conductive vias located along the cut line may beused, either alone or in combination with the lands. The buried vias maybe located so that the singulation cut leaves the walls of theconductive vias exposed resulting in vertical conductive strips, i.e.generally perpendicular to the PCB top and bottom surfaces 124A, 124B,in the PCB edge. Buried conductive vias may tend to fill with adhesiveduring fabrication of the PCB panel 124. Empty conductive vias, i.e.free of non-conductive adhesives, may be preferable for the resultingconcave conductive features, i.e. embedded conductive half cylinders.Similarly, solid buried conductive vias or conductive vias filled withconductive material during the PCB manufacturing process may bepreferable for the resulting continuous flat conductive surface.

In the alternative to buried conductive features, conductivethrough-holes, which are generally free of adhesives followingfabrication of the PCB panel 124 may be used along the cut line to forminterconnects extending through the thickness of the PCB from topsurface to bottom surface providing generally half-cylindricalinterconnects. A penalty of using through-holes for the interconnects isthe loss of surface area on the top and bottom of the PCB which mayotherwise be used for setback or other safety and agency approvalrequirements. Preferably, the through-holes may be filled, for examplewith a conductive material such as solder or silver paste, or conductivepins may be inserted into through holes and soldered to the throughholes, to prevent molding compound from filling the through hole duringthe encapsulation process and to provide a greater contact surface areayielding generally flat conductive interconnects following singulation.

The exposed interconnect features, e.g. 111A through 111L may be used tomake a variety of electrical connections. For example, the exposedinterconnects may be solder plated and then subsequently soldered to amotherboard, e.g. using surface mount soldering techniques. Theinterconnects may be soldered to a connector, such as connector 103shown in FIGS. 1, 13, 14. Alternatively, a lead frame or PCB may besoldered to the exposed interconnects 111, 112, 113 of the modulequickly after singulation. Yet another alternative includes a preciousmetal such as gold or silver or other suitable conductive materialdeposited to the exposed contacts, e.g. by plating, to build up thecontacts into a larger area, e.g. continuous conductive contacts, wellsuited to connectorized modules described in more detail below.

In the example shown in FIG. 11, the module 115 has interconnections 111along the edge 116 in which each interconnection 111 includes conductivefeatures, e.g., conductive lands 111A through 111L, formed along a cutline on a plurality of the conductive layers of the printed circuitboard to form a stack of conductive strips resembling a bar code aftersingulation. As used herein, a bar code or bar code terminal is a set ofone or more conductive features embedded in an edge of a PCB or othersubstrate that together form an electrical terminal for establishing aconnection to the PCB or substrate. For example, two bar codes 111, areshown in the close-up of FIG. 11. As shown, each bar code 111 includes aset of twelve conductive features, exposed conductive lands 111A-111L,which together form a single terminal of the module. In FIG. 10A, eightbar code terminals are shown formed in the edge 116 of PCB 104 providinga total of two power input (bar codes 113), two power output (bar codes111), and four signal (bar codes 112) connections for the module 115.

As described above, each conductive layer embedded in the PCB panel maybe patterned to ensure that a portion of it extends to the edge (e.g.,edge 116 in FIG. 10A) at first locations, i.e., in the regions (e.g.,regions 111, 112, 113 in FIG. 10A) in which the bar code terminals willbe formed, e.g., where it is intended to form a portion of the exposedinterconnect and be used to form an electrical connection to an externalterminal; and to ensure that no portion of the conductive layer extendsnear the edge at second locations where only insulative material isdesired, e.g., in areas free of electrical connections such as betweenthe terminals (e.g., between regions 111, 112, and 113 in FIG. 10A).Such setback requirements may be established to ensure that internalconductors do not inadvertently become exposed after the panels aresingulated or after further processing, allowing for manufacturingtolerances, e.g., maintaining a minimum distance, L, from the edges. Forexample, referring to FIG. 45, a portion of a PCB 920, e.g., internal toa panel molded and singulated module 940, is shown having a top 924conductive layer and a bottom 926 conductive layer, both of which areset back from the edge 928 (which is representative of the edge of theencapsulated module 940 after singulation) by a respective setbackdistance 927 to avoid exposure during module singulation and othermanufacturing processes.

In some implementations, it may be desirable to remove portions of theinsulation material around the conductive features making up a bar code,e.g., between and/or around the conductive lands (which may be PCBlayers or other suitable conductive features) of a bar code or otherembedded terminal to further increase the surface area of the conductivefeatures, e.g., for creating more robust electro-mechanical connections.For example the insulative material between or around the exposedconductive features may be removed, e.g., by etching, to exposeadditional surface areas of the portions of the conductive layers orconductive features at the first locations. The setback distance, L,discussed above may be chosen, with a suitable margin for safety, to begreater than the depth of etching of the insulative material to preventinadvertent exposure of unwanted portions of the conductive layers.

As shown in FIG. 46 the insulation material 922 adjacent to one or moreconductive layers at the edge 928 of the PCB 920 may be selectivelyremoved to form recesses 929 adjacent to the conductive features 930,exposing additional surface area of the exposed conductive features,e.g., along lateral portions of the conductive layers in the recesses929. The exposed portions 930 of the conductive layers may be referredto as exposed conductive features or 3D conductive features. Athree-dimensional (3D) conductive feature or terminal, as used hereinrefers to a conductive feature (such as an exposed conductive layer 930in FIG. 46) protruding from an edge of, or a recess in, a PCB or othersubstrate, e.g., having a contact surface area occupying more than twodimensions. Like the bar code terminals discussed above, the set ofexposed conductive features 930 also appear as a bar code terminal butwith an additional depth dimension. Note that in the example of FIGS. 45and 46, the ends of the exposed conductive features 930 remain flushwith the edge 928 of the module 940. In some examples, the etching ofthe insulation material 922 is selective so that only the insulationmaterial 922 around the conductive features 930 is etched. Athree-dimensional (3D) bar code or 3D bar code terminal, as used hereinis a set of 3D conductive features (such as exposed conductive layers930 in FIG. 46) protruding from an edge of, or a recess in, a PCB orother substrate that together form an electrical terminal forestablishing a connection to the PCB or substrate.

To make 3D bar codes from the conductive layers of a PCB as describedabove, the recesses in the PCB insulation should be formed using aprocess that selectively removes portions of the insulation layerwithout compromising other portions of the PCB or module. One method mayemploy a plasma etching process using for example, a Magna PCB EtchingSystem, available from Plasma Etch, Inc., Carson City, Nev., and/oretching equipment from other manufactures, such as Nordson March,Westlake, Ohio and PVA Tepla America, Corona, Calif. Such etchingequipment previously has been used in the PCB manufacturing industry forde-smear and etch back processing

In some implementations, surfaces of the module 940, including otherportions of the PCB 920, that are not to be etched, may be masked forprotection before the plasma etch is performed. Edges that have theexisting sawn 2D bar codes on them may be left exposed so the edges willbe etched. For the edge 928 that has the conductive features 930,portions of the edge 928 that have the conductive features 930 may beleft exposed, while portions of the edge 928 that do not have theconductive features 930 may be masked. This way, at the edge 928,portions of the insulation material 922 surrounding the conductivefeatures 930 will be etched, while portions of the insulation material922 away from the conductive features 930 will remain intact. Methods ofprotecting the PCB panel 920 can include aluminum tooling, polymer basedtooling, metalized tape systems, or other materials resistant to plasmaetching.

In some implementations, the etching process is performed under a vacuumof, e.g., approximately 100 mTorr. The Magna system may use an O₂ gaswhile other systems may use a mixture of CF₄ and O₂ gases. Using thePlasma Etch Magna System, parts are loaded into the system, oxygen gasis pumped into the system, the parts are presented into a uniform plasmaetching energy area, and the plasma gas is used to etch back the PCBlaminate. Spacing between the laminate layers such as 2 mils or 3 milsis controlled by the PCB design. The plasma breaks down the resin on theexposed edge. The duration of exposures determines the distance or depthof the etching process. For example, on a 3 mil copper layer to layerspacing, an etch into the laminate of 2.5 to 3.2 mils may be provided.For example, etch time may be in a range from 60 to 90 minutes. Theplasma does not significantly affect the dimensions of the exposedcopper, and in fact the effect on the dimensions may not be immediatelymeasurable.

Alternative methods of removing the insulation may include the use of alaser system with controlled focus to excavate or remove laminatebetween the conductive features. The incident angle of the laser beamwith respect to the work piece may be varied off the perpendicular, andmay be selected to etch the insulation without concern for shadowing bythe conductive layers. For example the incident angle may be set forplus and minus 45 degrees from the large planar surface of theconductive layers in the PCB to allow consistent etching of theinsulation between the conductive layers. Alternatively, the incidentangle of the laser may be varied continuously over a range, or may bemoved to predetermined set points during the etching process. The laserbeam may be moved in various patterns, e.g., a raster, across thesurface to achieve uniform excavation.

After etching, a media blasting system may be used to remove anyremnants of the etched insulation and also clean the exposed surfaces ofthe conductive features. For example, a system such as a Cold Jet I3MICROCLEAN, available from Cold Jet New Zealand Ltd, Auckland, NewZealand, can be used to clean out the ash and remaining fiberglassfibers in the etched recesses generated between the exposed conductivefeatures, e.g., between the conductive layers forming the 3D bar code.Dry ice CO₂ can be used as the blast media to remove the ash and fibersin the etch areas between the conductive layers. The particles need tobe able to fit in the spaces generated between the conductive layers sothe laminate residue is cleanly and evenly removed. The system may alsoremove any oxide present on the surfaces of the conductive layer. Dryice is advantageous for its low residue forming quality, but othermechanical media blast particulates can also be used as alternatives.Alternatively, a fine bristle brush can be used to remove the laminateresidue.

The 3D bar codes produced by the above described methods have exposedconductive surfaces that are solderable and may be protected after theetch, or etch and ablation, process with a solder coating by a tinningor wave solder process, or using an organic solder preservative, orelectroless nickel-immersion gold (ENIG), or application of othersuitable coatings. Solder paste may be applied with some force to fillthe recesses and then re-flowed. Alternatively, the exposed conductivefeatures may be wetted with solder.

G1. Vertical Mount Connector

Referring to FIGS. 1, 13 and 14, a connector 103 suitable for attachmentto the edge 116 of the module 115 is shown having a connector body 118with a plurality of recesses 117 and a plurality of holes 119A, 119B,and 119C. A plurality of connector pins 108, 109, 110 may be insertedinto holes 119A, 119B, 119C, respectively, from the top 118A. As shown,the holes may be contoured to provide a pressure fit having a grippingforce suitable for retaining the pins. The broad top surfaces 108A,109A, 110A of the pins are suitable for making solder connections to theexposed interconnects 111, 113, 112, respectively on the edge 116 of thePCB 104 of module 115. As shown, the recesses 117 provide countersinkingfor the top portions of the pins allowing the connector body to mountflush to the edge 116 of module 115 and allowing space for a solderjoint between the pin and the respective interconnect. Theinterconnection features may preferably be provided along a long edge ofthe module 115 yielding a more stable vertical mount module 100 such asshown in FIG. 1. However, the interconnection features may be deployedalong any or all of the edges of the module 115 for different mountingconfigurations as discussed more fully below.

G2. Horizontal Through-Hole Mount

Referring to FIGS. 15 and 16, a horizontal mount component 200 suitablefor through hole mounting in a motherboard is shown including asingulated module 215 and through-hole adapters 203A, 203B. Thehorizontal mount module 200 may be constructed in the same manner asdescribed above for the module 100, except that the interconnects arepreferably disposed along two edges of the module PCB and connectorsadapted for horizontal mounting may be used. As shown in FIG. 16, theinterconnects are disposed along the two shorter edges of the PCB 204 inmodule 215. However, the longer edges may be used instead of, or inaddition to, the shorter edges for the interconnects. Although only oneset of the interconnects 211, 212 is visible in the perspective view ofFIG. 16, it will be understood that a second set, including twoadditional power interconnects, is disposed along the opposite hiddenedge of the PCB.

Through-hole adapters 203A and 203B, suitable for attachment to theedges of the singulated module 215 are shown having adapter bodies 218supporting conductive terminals 208, 210 and 209, respectively. Aportion of each terminal may be exposed on an internal surface via anopening in the adapter body optionally providing a small recess. In FIG.16 for example, adapter 203B is shown having two power terminals 209,each having an exposed areas 209A recessed in openings in surface 218Aof the adapter body 218. The exposed areas 209A align with theirrespective interconnects when the adapters 203A, 203B are assembled ontothe module 215. The recesses provide countersinking for the exposedterminals allowing the internal surface 218A of the adapter body 218 tomount flush to the edge of module 215 and allowing space for a solderjoint between the terminal and the respective interconnect. The adapterbody 218 may include a flange 218B which may form a pressure fit withthe adjacent edges of the modules 25. Additional features may beprovided for maintaining the structural integrity of the module andconnectors.

As shown in FIG. 16, epoxy may be deposited along an internal edge ofthe connector body, e.g. in the shaded area 219 preferably aligned withthe encapsulant layer 206 to secure the adapters 203A, 203B to themodule 215. The horizontal mount module 200 may be readily adapted tomatch industry standard brick footprints for power converters, inparticular the module 200 may fit within the standard ⅛^(th) brickfootprint.

G3. Horizontal Surface-Mount

Referring to FIGS. 17 and 18, a horizontal-mount component 300 suitablefor surface-mount soldering to a motherboard is shown including asingulated module 315 and surface-mount adapters 303A and 303B. Thehorizontal-mount module 300 may be constructed in the same manner asdescribed above for the module 200 (FIGS. 15, 16) substituting surfacemount adapters 303A, 303B for through-hole adapters 203A, 203B. As shownin FIG. 17, the singulated module 315 may have flat heat sinks 301, 302instead of the finned heat sinks (shown in FIGS. 1-4, 6-12, 15-16).Although shown disposed along the two shorter edges in FIGS. 17 and 18,the interconnects may be deployed along the longer edges of the PCB 304in the singulated module 315 instead of, or in addition to, the longeredges.

In FIGS. 17 and 18, the surface-mount adapters are shown with smallerbodies 318 than the through-hole adapters (218: FIG. 15, 16) exposingthe connections between the terminals and their respective interconnectsduring assembly and for post assembly inspection. The terminals 308,309, 310 each may include a portion, e.g. solder pads 308A, 310A, 309A,adapted for connection, such as a solder joint, to a respectiveinterconnect on the module, e.g. interconnect 311, 312, and 313 (notvisible in FIGS. 17 and 18). Holes 308B, 309B, 310B may be provided insolder pads 308A, 309A, 310A for better solder joints. Each terminal308, 309, 310 may include a bend (e.g. 308C) to produce a surface-mountpad (e.g. 308D) for attachment, e.g. by surface-mount soldering, to acustomer motherboard.

The adapter bodies 318 may include flanges 318B, preferably along two ormore sides to form a pressure fit with the adjacent edges of the modules315. Additional features may be provided for maintaining the structuralintegrity of the module and adapters. As shown in FIG. 18, epoxy may bedeposited along an internal edge of the connector body, e.g. in theshaded area 319 preferably aligned with the encapsulant layer 306 tosecure the adapters 303A, 303B to the module 315.

G4. Surface-Mount Lead Frame

An alternate embodiment of a horizontal-mount component 400 suitable forsurface-mount soldering to a motherboard is shown in FIGS. 19 and 20including a singulated module 415. The horizontal-mount module 400 maybe constructed in the same manner as described above for the module 300(FIGS. 17, 18) substituting lead frame adapter 403 for the surface-mountadapters 303A, 303B. Like module 315 (FIG. 17), the singulated module415 may have flat heat sinks 301, 302 instead of the finned heat sinksof the previous examples. However, in the example of FIGS. 19 and 20,the interconnects are shown deployed along the longer sides of thesingulated module 415. However, as noted above the interconnects may bedeployed along any edges of the PCB 404 as desired in the singulatedmodule 415.

The surface-mount adapter is shown in FIGS. 19 and 20 having a unitaryrectangular frame-like body 418 supporting a plurality of terminals 408.The profile of the frame body 418 may as shown leave a portion of theterminals exposed for making connections to their respectiveinterconnects during assembly and for post assembly inspection. Theterminals 408 each may include a portion, e.g. solder pad 408A, adaptedfor connection, such as a solder joint, to a respective interconnect onthe module (not visible in FIGS. 19, 20). Although shown without holesin FIG. 19, the solder pads may optionally include holes such as thoseshown in FIGS. 17 and 18. Each terminal 408 may include a bend (e.g.408C) to produce a surface-mount pad (e.g. 408D) for attachment, e.g. bysurface-mount soldering, to a customer motherboard.

The opening in the frame body 418 may be sized to accommodate theperimeter edges of the singulated module 415 and optionally form apressure fit. The frame body 418 may include recesses 417 foraccommodating the terminals 408, allowing the interior surface 418A ofthe frame body 418 to rest flush against the module 415 surface.Additional features may be provided for maintaining the structuralintegrity of the module and adapters. Gaps may be provided in theinterior surface 418A to allow the application of epoxy to secure theframe body 418 to the module 415.

G5. Connectorized Module

The modules 100, 200, 300, and 400 discussed above in connection withFIGS. 1, and 15-20 are all examples in which connectors or adapters aremechanically and electrically connected to the interconnects on thesingulated modules forming an integral modular component. Yet anotheroption is to adapt the module to be removably mated with a connectorthat may be mounted on a customer circuit board. For example, the moduleinterconnects may be plated up with an appropriate conductive material,such as silver or gold, to form contacts that may be reliably engagedwith connector contacts, i.e. “connectorized.” Referring to FIGS. 21 and22, a module-connector set 500 is shown including a connectorized module515 in exploded view with a mating connector 503 into which the module515 may be removably inserted.

The connector 503 as shown includes a body 518 having side walls 518Bcreating an opening 518C adapted to receive the connectorized module515. Terminals 508 formed, e.g. bends 508B (FIG. 22), to provide apressure fit between a contact area 508A of each terminal 508 and arespective interconnect 511. The terminals as shown may be retained inrecesses 517 in the interior surface 518A of the side walls 518B. Therecesses 517 may provide support to keep the terminals 508 in place andallow the interior surfaces to engage the surfaces of the module 515.The terminals 508 may include a flat portion 508D (FIGS. 22, 23) adaptedfor making a solder connection to surface contacts on a customer circuitboard (not shown). The connector body may include a bottom surface 518Denhancing the structural integrity of the connector walls 518B which aresubjected to the forces exerted by the terminals 508 against theinterconnects 511. The bottom 518D may include openings as shown in FIG.23 through which the terminals may be inserted during assembly of theconnector 503. The bottom 518D may provide electrical insulation betweenthe metal heat sink 502 and the customer circuit board (not shown) onwhich the connector 503 may be mounted. Alternatively, the bottom may bepartially or completely removed to allow better conduction of heat fromthe module 515 out through the customer circuit board. Yet anotheralternative is to use a thermally conductive material in the bottom 518Dof the connector 503. FIG. 24 shows the connectorized module 515inserted into the connector 503.

As shown, the connector terminals 508 exert inward pressure fromopposing ends of the module, however, the contacts may be arranged alonga single side of the module with the connector body providing thenecessary resistive force for the pressure fit. Although theconnectorized module is shown having plated interconnects 511 formingcontacts for engagement with the connector terminals, it should beappreciated by those of skill in the art that many variations arepossible. For example, adapters of the type illustrated in connectionwith FIGS. 15-20 may be used to provide contacts for a hybridconnectorized module allowing other orientations of the module relativeto the connector and to the customer circuit board.

G6. Flush Mount

A flush-mount technique may be used with the horizontal PCB-mountingtechniques discussed above in connection with FIGS. 15-24 to allow thebottom heat sink to come into contact with the customer PCB, e.g. forheat removal. As shown in FIGS. 25 and 26, a through-hole mount module600 is shown adapted for flush-mounting to a customer PCB 900. Themodule 600 as shown includes two through-hole adapters 603A, 603Battached to the singulated module 615. The singulated module 615 may, asshown, have a finned top heat sink 601 and a generally flat bottom heatsink 602 for flush mounting against the PCB 900. Similar to the adaptersdiscussed above in connections with FIGS. 16-20, through-hole adapters603A, 603B have terminals, 608, 609, 610 which include features, such assolder pad 608A, adapted to be attached, e.g. by solder, to respectiveinterconnects on the module 615. The terminals 608, 609, 610 may beadapted to be soldered into through holes 908, 909, 910, respectively,in the customer PCB 900. As shown in FIGS. 25 and 26, the generally flatheat sink 602 may include recesses 602B to accommodate flanges 618B ofthe adapter bodies 618 allowing most of the surface of heat sink 602 torest flush against the surface of the PCB 900. Epoxy or other adhesivemay be used in the recess to secure the adapter body to the module. Therecesses may be an integral feature of the heat sink panel or may beadded at an appropriate point during the manufacturing process,preferably before singulation.

A thermally conductive material 901, e.g. thermal adhesive, may beapplied between the PCB 900 and the module heat sink 602 to facilitateremoval of heat through the PCB 900. Additionally, the PCB surface mayinclude thermally conductive features to conduct heat away from themodule 615. For some applications particularly involving smaller modulesizes, it may be desirable to solder the bottom heat sink 602 to one ormore pads on the PCB 900, in which case the heat sink may include asolderable finish, applied for example by plating. Threaded holes may beprovided, preferably in the flush mount heat sink panel, allowing themodule to be secured using screws to a customer board or cold plate. Theflush-mount modification may allow taller heat sink fins to be used onthe top of the module without increasing the module profile above thecustomer PCB which may provide better thermal management in someenvironments. Additionally, the flush-mount may provide a more robustshock and vibration resistant mechanical solution.

Another flush mount module 650 may include a plurality of pins 661protruding from the bottom heat sink 652 for engagement in through holes911 in the customer mother board 900 as shown in FIG. 25A. Similar tothe flush mount module 600 of FIGS. 25 and 26, the flush mount module650 may include adapters 653A and 653B adapted for making electricalconnections with through holes on the customer mother board 900. Insteadof fins, the top heat sink 651 may include a flat surface to create alow-profile package as shown in FIG. 25A. The pins 661 may be formed asan integral part of the bottom heat sink panel instead of fins.Alternatively, blind holes may be provided in the heat sink panel intowhich the pins may be press fit at any suitable stage of the fabricationprocess. The pins 661 may be used to electrically connect the bottomheat sink 652 to the customer board, e.g. to ground, conduct heat out ofthe module into the customer board 900, and provide mechanical support.The through holes 908, 909, 910, 911 in the customer board may be sizedto provide clearance between the hole and the respective pin tocompensate for any dimensional variations. The pins 661 may optionallyprotrude beyond the bottom surface of the customer board 900 into forcedair along the bottom surface of the board for additional heat removal.Additionally, a heat sink component (not shown) may be fitted onto theprotruding pins to help dissipate heat.

H. Heat Sink Setback

As internal components are reduced in height, e.g. reducing thethickness of the magnetic core, the depth of the interior cavity may bedecreased bringing the heat sink panels closer together, reducing theencapsulant thickness and the resulting module thickness. However,reduction of the encapsulant thickness has the potentially undesirableeffect of reducing the spacing between the electrical interconnects andthe edges of the heat sink panels in the finished module. Whendesirable, e.g. to satisfy safety agency requirements, the separationbetween the exposed interconnects, e.g. interconnects 111, 112, 113, andthe edge of the heat sink, e.g. heat sink 101B, may be increased using asetback, e.g. setback 155, between the edges of the heat sink panels andthe edges of the module 115B as shown in FIG. 10B. The setback 155 maybe created by making wide cuts through the heat sink panels 121, 122along the singulation lines prior to singulation. The wide cutspreferably extend through the heat sink material, e.g. aluminum, andpartially into the encapsulation material to form channels 128A and 129Ain the panel assembly 120A as shown in FIGS. 9B and 9C. If machinedwhile the assembly is still hot from the encapsulation process, thechannels 128A and 129A may be used to divide the heat sink panels intosingulated module dimensions reducing stresses due to differentialcontraction between the heat sink and the encapsulant due to differencesin thermal coefficients of expansion while the panel assembly cools.Stresses on the narrow saw may also be reduced by eliminating the heatsink metal through which the saw must cut during singulation as a resultof the channels 128A, 129A.

I. Process Efficiencies

Using interconnection features that may be exposed during singulationallows the PCB panel 124, containing a plurality of modules, to bemolded as a single unit. Providing embedded interconnects along theperimeter of the circuit that occupy little or no PCB surface area helpreduce wasted PCB area that would otherwise be cut away, allowing closeto full utilization of the PCB for product which may save on cost.Encapsulating the PCB panel with the heat sink panels simplifies thestructural aspects of the modules. Using interior contours in the heatsink to match component heights helps reduce the amount of moldingcompound required for encapsulation. Furthermore, controlling thedistance between the magnetic cores and the internal surface of the heatsink can be used as an alternative to and eliminating the complicationsof the exposed core molding process described in the Exposed CoreApplication.

Furthermore, using the mold panels to form the mold cavity forencapsulating the PCB panel helps free the molding equipment fromproduct specific requirements that may otherwise require customizedmolds, allowing a single piece of molding equipment to be used for awide variety of product mixes. The finished products, e.g. modules 115made using a standard panel size, may have diverse dimensions not onlyin the lateral (length and width) directions, but also in the vertical(thickness) direction (e.g. due to heat sink fin height or componentthickness). However, because the lateral panel dimensions remain thesame, and variations in thickness from panel to panel may beaccommodated by the molding press, the same general purpose moldingequipment may be used for a wide variety of products of diversedimensions. Using power converters as an example, the same mold pressmay be used to encapsulate panels of power converters ranging in (1)footprint size from full size, to half, to quarter, to eighth size (orany other size), and in (2) thickness (height), and in (3) topology,e.g. isolated DC-DC regulating converter, non-isolated buck regulator,DC transformer, etc. to produce a large mix of products.

A panel molding manufacturing process for a mix of products may includesome or all of the following steps. Select a specific product to build.Select the requisite blank heat sink panels, e.g. based upon finorientation, spacing, and height for the specific product.Alternatively, machine the exterior of the heat sink blank panels toproduce the requisite external surface (heat sink surface, mountingfeatures such as threaded holes, fin orientation, thickness, andspacing). Machine the interior surfaces of the heat sink blanks to formthe recesses and other features (i.e. the contours of interior cavity tomatch some or all component locations, size, and height), of thefinished heat sink panels required for the specific product, preferablyunder computer control. Select the appropriate PCB panel for thespecific product. Select and assemble the magnetic cores and othercomponents onto the PCB panel, e.g. by surface mount soldering, etc.Dispense a measured quantity of molding compound into the bottom heatsink panel. Press the bottom side of PCB panel up against bottom heatsink panel. Dispense a measured quantity of molding compound on the topside of the PCB panel. Press top heat sink panel into place on the PCBpanel. Place the panel assembly on a rotary table away from the axis ofrotation, preferably a large distance from the axis, and spin the rotarytable and panel assembly to evacuate air bubbles in the interior cavityto achieve essentially void free fill of panel assembly with moldingcompound. Cure the molding compound. Cut the panel along the cut linesfor singulation. Apply a conformal coating to protect the interconnects,or plate the interconnects, or attach a lead frame, motherboard, orconnector to the exposed interconnects.

J. PCB Symmetries

The components may be symmetrically arranged on the PCB such as shown inthe power converter example of FIG. 27. The top 104-2 and bottom 104-1faces of a populated PCB 104 from an individual power converter moduleare shown in plan view in FIG. 27. The populated PCB 104 is shownrotated along the vertical axis 27 in FIG. 27 to show the symmetry ofthe components.

J1. Symmetrical Distribution Between PCB Surfaces

Many of the larger components may be distributed equally between bothfaces of PCB 104 as shown in FIG. 27. For example, the four input fieldeffect transistors (FETs) 132-2D, 132-2E, 132-1D, 132-1E are shownequally distributed between the top 104-2 and bottom 104-1 surfaces withtwo FETs on each surface. Similar equal distribution between the top104-2 and bottom 104-1 surfaces of the PCB 104 are shown for the eightoutput FETs 132-2B, 132-2C, 132-1B, 132-1C with four output FETs on eachsurface; the twelve input capacitors, 132-2F, 132-2G, 132-1F, 132-1G,with six input capacitors on each surface; and twenty four outputcapacitors 132-2A, 132-1A with twelve output capacitors on each surface.Some of the FETs can function as switches. Distributing largercomponents between the two surfaces of the PCB may decrease stresses onthe PCB, e.g. due to differences in the coefficient of expansion of theencapsulant, e.g. while curing, which may improve the co-planarity andmechanical integrity of the device.

J2. Symmetrical Distribution on a PCB Surface

On each surface of the PCB, components having similar characteristics,such as size or in-circuit power dissipation, may be arrangedsymmetrically for example as shown in FIG. 27 with respect to horizontalaxis 28. It can be seem that relative to the horizontal axis 28, whichis drawn longitudinally through the midline of the top and bottomsurfaces of PCB 104, many of the components are arranged symmetrically.For example, the six input capacitors 132-1F and 132-1G on the bottomsurface 104-1 are symmetrically distributed in a mirror-imagerelationship to each other relative to longitudinal midline axis 28. Thesame basic mirror image relationship is true for the six inputcapacitors 132-2F and 132-2G on the top 104-2 surface of the PCB.Similarly, the mirror image relationship is shown for the followingpairs of components: bottom-side input FETs 132-1D and 132-1E, topsideinput FETs 132-2D and 132-2E, bottom-side output FETs 132-1B and 132-1C,topside output FETs 132-2B and 132-2C and also within the bottom-sideand top-side banks of output capacitors 132-1A and 132-2A.

Distributing larger components symmetrically on a surface especiallywith respect to the longitudinal axis of the PCB may also decreasestresses on the PCB, e.g. due to differences in the coefficient ofexpansion of the encapsulant, e.g. while curing, which may also improvethe mechanical integrity of the device. Additionally, spreading thecomponents out symmetrically on each surface helps to spread the heatproduced by power dissipating devices using a greater surface area forheat extraction improving the thermal performance.

J3. Symmetrical Footprints Between PCB Surfaces

In addition to being equally distributed between the top and bottomsurfaces and being symmetrically distributed on each PCB surface, thecomponents may also be situated such that pairs of components (whereineach component on one surface has a respective counterpart on the othersurface) may be arranged to occupy essentially the same space on thePCB, i.e. a component may occupy a space on one surface thatsubstantially overlaps with the footprint of a component on the othersurface. For example, input capacitors 132-1F on the bottom surface arein the same position as their counterparts 132-2F on the top surface,i.e. they share the same footprint on the PCB. The same relationship isgenerally true for: input capacitors 132-1G and 132-2G; outputcapacitors 132-1A and 132-2A; input FETs 132-1D and 132-2D; input FETs132-1E and 132-2E; output FETs 132-1B and 132-2B; output FETs 132-1C and132-2C; in which the pairs of components occupy the same basicfootprint, albeit on opposite surfaces, of the PCB. One benefit ofsharing footprints allows the pair of components to share a common setof conductive vias used to electrically connect the components on thePCB surfaces to internal conductive layers, e.g. used to form thewindings of the transformer. Because each via is used for bothcomponents in the pair, the total number of vias for making connectionsto the pair of components may be reduced (by as much as a factor of two)increasing the area of conductive layers useable for making connectionsand thus reducing resistance. For example, assuming 6 vias are requiredfor each output FET (a total of 12 vias for two FETs), using symmetricalfootprint approach, the pair of FETs can share the same 6 vias (withoutincreasing the via resistance) and because the number has been reducedthe useable area for conductors may be increased. Alternatively, whilereducing the total number of vias from 12 to some intermediate number,e.g. 8, the resistance of the vias may be decreased because of theincrease in effective vias per FET while still increasing the areauseable for conductors.

J4. Symmetrical Power Dissipation Between PCB Surfaces

The components may be arranged between the PCB surfaces according toheat dissipated during operation. For example, the heat dissipativecomponents may be arranged in a manner that distributes the heat evenlybetween the two PCB surfaces allowing heat produced by power dissipatingdevices to be extracted from both surfaces of the PCB improving thethermal performance. This type of heat dissipation symmetry is alsofactored into the component layout shown in the power converter of FIG.27. For example, two input cells each using the same basic circuittopology are shown, one above and another below axis 28. As shown, thecomponents of each input cell occupy both sides of the PCB in observanceof other factors influencing component layout such as winding locations,etc. In this example, the upper input cell includes the two input FETs132-1D and 132-2D, and the six input capacitors 132-1F and 132-2F. Thelower input cell includes the two input FETs 132-1E and 132-2E, and thesix input capacitors 132-1G and 132-2G. To ensure heat dissipationsymmetry between the two surfaces, the cells may be arranged in mirrorimage layouts as shown. In FIG. 27, input FET 132-2E (top surface) inthe lower cell corresponds to input FET 132-1D (bottom surface) in theupper cell. Similarly, lower cell input FET 132-1E (bottom surface)corresponds to upper cell input FET 132-2D (top surface). As can beseen, the significant power dissipative components of the input cellsare arranged to have one component of one cell mounted on one surfacewith the respective component from the other cell mounted on the othersurface. This type of symmetry may be seen in FIG. 27 with lower cellcomponent 132-2H mounted on the top surface and the respective uppercell component 132-1H mounted on the bottom surface. In some examples,the FETs are arranged such that during operation, the power FETs on thetop surface dissipate power at a level that is comparable to the levelof power dissipated by the power FETs on the bottom surface. Also, thelevel of power dissipated by the power FETs in the upper input cell iscomparable to the level of power dissipated by the power FETs in thelower input cell. For example, the level of power dissipated by thepower FETs on one surface is less than 150% of the level of powerdissipated by the power FETs on the other surface. The level of powerdissipated by the power FETs in the upper cell is less than 150% of thelevel of power dissipated by the power FETs in the lower cell, and viceversa.

Laying out the components using any or all of the above symmetriesproduces several key benefits including, enhanced thermal performance,reducing top to bottom and side to side imbalances during encapsulationcaused by asymmetrical distribution of components may enhance theco-planarity and structural integrity, and shared component footprintson top and bottom PCB surfaces may help reduce conduction losses andincrease efficiency.

K. Center Plate Panel Assembly

In an alternate embodiment, an optional center plate 727 may be usedbetween the top 721 and bottom 722 heat sink panels as illustrated inFIG. 28 through FIG. 32. The center plate 727, which may be made fromaluminum, a molded high temperature plastic or any other materialsuitable for the molding process, includes an opening 729 in which thepopulated PCB panel 724 may sit during the panel molding process. Asshown in the side view of FIG. 29 and the cross-sectional view of FIG.32, the PCB panel 724 may sit entirely within the opening 729 and mayhave some high profile components, such as magnetic cores 131 andcapacitors 132 (continuing with the power converter example), extendingbeyond the planar surfaces of the center plate. Alternatively, thecenter plate may be made thick enough, or include a ridge around theperiphery tall enough, such that the PCB panel and all components sitentirely within the opening allowing a flat surface (heatsink panel ormold panel) to close against the center plate. The recesses formed inthe interior surfaces of the heat sink panels 721, 722 (described above)may accommodate portions of the components extending beyond the centerplate surface. Conversely, protrusions from the interior surface of theheat sink panels may be used to reduce the distance between the heatsink and lower profile components. However, it may be preferable forease of fabrication and tolerance control to avoid protrusions of theheat sink beyond the surface of the center plate which may put an upperlimit on the thickness of the center plate in some embodiments.

As shown in the exploded perspective view of FIG. 28 and the top planview of FIG. 31, registration features may be provided in the centerplate 727. For example, registration pins 728 may mate withcorresponding holes 734 in the PCB 724 to establish the horizontalposition, i.e. in the X and Y directions, of the PCB relative to thecenter plate 727. Additional registration features such as theillustrated horizontal shelf 728A (FIG. 28), may be provided toestablish the vertical position, i.e. in the Z direction, of the PCBrelative to the center plate. The registration pins 728 may be longenough to extend beyond the upper surface of the PCB panel 724 in theupward direction and beyond the horizontal shelf in the downwarddirection to mate with holes (analogous to holes 152 and 153 in FIG. 4B)which may be provided in the top and bottom heat sink panels 721, 722establishing the horizontal positions of the mold panels relative to thecenter plate 727. Provision of the registration features in the centerplate may help relax certain precision requirements, the complexity, andthus the cost of the heat sink panels.

A cross-section of the panel assembly 720 closed in a mold press takenthrough line 32-32 in FIGS. 30 and 31 is shown in FIG. 32. As shown, theupper mold press 761 engages the center plate 727 directly along itsperimeter in regions 768 and engages the heat sink panels directly alongtheir perimeters in regions 769. Preferably the mold press includesrecessed surfaces 766 providing cavities 765 large enough to accommodatea full range of fin heights (or other heat sink panel features)supporting a diverse range of products. To compensate for dimensionaldifferences between the thickness of the heat sink panels in regions 769and the difference in elevation between interface regions 768 and 769 inthe mold press, one or more compressible features may be provided at theinterface between the heat sink panels 721, 722 and the center plate727. For example, a small crushable feature 723 may be formed along theperimeter of and as an integral part of the heat sink panels asillustrated in FIG. 32. Alternatively a gasket may be used between thecenter plate and one or both of the heat sink panels. As the presscloses on the panel assembly 720 the crushable features 723 arecompressed until the press is closed securely against both the centerplate 727 and the heat sink panels 721, 722. As shown in FIG. 31, thecrushable features may extend along the perimeter of the interior cavityforming a seal between each heat sink panel and the center plate.

The center plate may preferably include an extension, e.g. extension730, to at least one side of opening 729 providing space for one or morechambers 725 as shown in FIGS. 30, 31, and 32. During the transfermolding process, encapsulation material may be forced from the chambersthrough one or more channels 726 (as shown in FIGS. 28 and 32) in thecenter plate into opening 729 and thus the cavity in which the populatedPCB panel 724 is enclosed. An example of encapsulant flow through achamber 725, channel 726, and into the interior cavity 746 isillustrated by the arrows 767 shown in FIG. 32.

In the center plate panel mold assembly, the top and bottom mold panels(i.e., heat sink panels 721, 722) close against the center plate insteadof each other, reducing the thickness of the top and bottom mold panels,increasing the symmetry between, and reducing the complexity of, the topand bottom heat sink panels 721, 722, potentially simplifying themolding press, eliminating critical tolerance accumulations in theassembly, simplifying the process and reducing cost. For example,provision of the chambers 725 and conduits 726 in the center plate 727eliminates the need for sealing along a second axis, e.g. in ahorizontal direction and allows for use of a simpler cull-on-platemolding press. Critical tolerances are reduced to the one verticaldimension of the heat sink panels which can be relaxed using a crushablefeature or a compliant material on the surface that interfaces with thecenter plate. Additionally, the center plate 727 may be standardizedallowing a single configuration to be used with a large variety of heatsink panels such that the center plate may be cost-effectively molded.

III. Molding Process Non-Integrated Re-Useable Mold

A. Components without Heatsinks

In some applications it may be desirable to use the panel-moldingprocess to produce components, such as power converters, without theflat heat sink surfaces (FIGS. 17-24, 25, 26), finned heat sinks (FIGS.1, 10, 12, 15-16, 25, 26), or pinned heat sink (FIG. 25A) featuresdescribed in the above embodiments. Referring to FIGS. 33 and 34, ahorizontal-mount component 800 is shown including a singulated module815 and two adapters 803A, 803B, suitable for through-hole mounting to amotherboard. Comparing the singulated module 815 (FIG. 33) with thesingulated modules 215 (FIG. 16) and 315 (FIG. 17) reveals that theintegral heat sink surfaces of the previous examples are omitted in thesingulated module 815. As shown in FIGS. 33 and 34 and described ingreater detail below, the top 815A and bottom 815B surfaces of thesingulated module 815 are defined by the cured encapsulant 805, 806 inwhich the magnetic core surfaces 815C, 815D are exposed.

Like the singulated modules with heat sinks, various types of connectorsor adapters may be coupled to the exposed interconnects 811, 812 at theedges of the singulated module 815. All of the variations describedabove in connection with the heat-sink versions may be adapted for usewith the singulated module 815. As shown in FIGS. 33 and 34, adapters803 having terminal portions 808 and interconnect portions 808A may beformed for example by a precision metal stamping process. Initially, theterminal portions 808 may be coupled to a lead frame 808B as shown inFIGS. 35 and 36 forming a unitary unit for ease of assembly. Theinterconnect portions 808A may be soldered to the exposed interconnects811, 812 in the manner described above, and protective caps 818 may beattached, e.g. with epoxy, covering the interconnect portions 808A, toprovide structural integrity, and exposing only the terminals 808. Thelead frame 808B may be separated from the terminals 808 after theterminals are attached to the exposed contacts.

B. Center Plate Molding

The above-described panel molding process may be adapted to produce theheat-sinkless modules 815 shown in FIGS. 33 through 36. Referring to theexploded view of FIG. 37, re-useable flat top and bottom plates 834 maybe used in place of the top and bottom heat sink panels of the previousexamples. The center plate 827, which like the center plate 727 in FIG.28 may be made from aluminum, a molded high temperature plastic or anyother material suitable for the molding process, includes an opening 829in which the populated PCB panel 824 may sit during the molding process.Like the example of FIG. 28, the center plate 827 may include anextension, e.g. extension 830 in FIG. 38, to at least one side ofopening 829 providing space for one or more chambers 825 (shown in FIGS.37, 39, and 40).

The center plate 827 may include a sealing ridge 823 along the peripheryof the opening 829 to provide a total thickness of the center plate 827sufficient to accommodate the PCB panel 824 and all of the components,including for example the magnetic cores 131, while minimizing wastematerial in the center plate. Referring to the side view of FIG. 38, thethickness of the manifold provides adequate clearance for all of thecomponents on the PCB panel 824. As shown in the cut away section827A-827A in FIG. 38, the space between the cores and the plates 821,822 may preferably be minimized, reducing the volume of encapsulantrequired. The plate registration pins 828 are shown in FIG. 38protruding above and below the centerplate sufficiently to engage matingopenings 834 provided in the top and bottom plates, 821, 822.

The PCB panel 824 may be seated on registration shelves 828B (FIG. 37)for establishing the correct vertical positioning of the PCB panel withrespect to the manifold 827. The horizontal position of the PCB panelmay be established using the registration pins shown in the previousexample (e.g. pins 728 in FIG. 28), or may be accurately placed in theopening, e.g. using pick and place equipment or a fixture, and affixedto the center plate, e.g. using epoxy, e.g. deposited on theregistration shelves 828B prior to placement of the PCB panel. The useof an adhesive such as epoxy helps to prevent bowing of the PCB panel asmold compound is forced into the cavity during the molding process.Venting features 823A may be provided in the sealing ridges 823 alongthe side opposite where the mold compound is injected into the cavity asshown in FIGS. 37 and 39.

Referring to the FIG. 40, a section of the panel assembly 820 (takenalong lines 40-40 shown in FIG. 39) is shown closed in a mold press. Themold press includes an upper press 861 and a lower press 862 which closedirectly against the center plate 827 along its perimeter forming seals868 as shown. The mold presses 861, 862 may include recessed surfaces864 creating cavities 865 large enough to accommodate a full range ofPCB panel heights, supporting a diverse range of products. Shim plates863 may be used between the recessed surfaces 864 of the mold presses861, 862 and the top and bottom plates 821, 822 to force the platesagainst and form a seal with the center plate 827, e.g. along sealingridges 823. For example, mold-to-shim-plate interface 869A andshim-plate-to-plate interface 869B are shown in FIG. 40. Variations inthickness of the center plates 827 are accommodated by the mold pressclosing directly against the center plate 827. Variations in the heightof the top or bottom plate from the respective center plate surface maybe accommodated by varying the thickness of the respective shim plate.In this way, components of varying thicknesses may be produced using ancenter plate 827 having the appropriate thickness for the desiredcomponent height and using thicker or thinner shim plates 863 asnecessary to adjust for any difference in height between the centerplate 827 and the top and bottom plates 821, 822. Alternatively, one orboth of the shim plates may be omitted completely allowing the moldpresses to press directly against the respective top and/or bottomplates.

During the transfer molding process, encapsulation material may beforced from the chambers 825 through one or more channels 826 (FIG. 40)in the center plate into opening 829 (FIG. 37) and thus the cavity inwhich the populated PCB panel 824 is enclosed. An example of encapsulantflow through a chamber 825, channel 826, and into the cavity isillustrated by the arrows 867 shown in FIG. 40. After the encapsulant iscured, e.g., by heating, the manifold plate 827 and the encapsulated PCBpanel may be separated from the upper and lower mold presses 861, 862.During or after the cooling process, the top and bottom plates may beremoved from the panel assembly. The surfaces of the top and bottomplates 821, 822 are relatively smooth and separate easily from theencapsulant as the panel assembly cools due to differences in thermalexpansion coefficients of the materials.

FIG. 41 shows a top plan view of the encapsulated panel assembly 820Aseparated from the upper and lower mold presses after removal of the topand bottom plates 821, 822. The center plate 827 may includeregistration features 828A (FIGS. 37, 39, 41) for positional accuracy inpre- and post-encapsulation processing of the panel. For example, theregistration features 828A may be used to accurately position the PCBpanel with respect to the center plate during installation or may beengaged by pins in the mold to accurately position the center plate inthe mold. Greater positional accuracy may be achieved by making one ormore holes 871 through the encapsulant in predetermined regions of theencapsulated PCB to expose corresponding fiducial marks 872 incorporatedin the PCB panel. The center plate 827 and its registration features828A thus may be used to establish an approximate horizontal position(of the PCB panel) for making the holes 871 which preferably would belarger than the fiducial marks 872. The exposed fiducial marks may beused to register the position of the PCB panel with greater accuracy forprecise singulation. FIG. 42 shows a cross-sectional view of theencapsulated panel assembly through one of the holes 871 in theencapsulant exposing the fiducial mark 872 on the PCB panel.

Preferably before singulation, the encapsulated panel assembly may belapped to expose the magnetic cores, finish the surface, and accuratelyestablish the thickness of the panel-molded components. Aftersingulation, the interconnects may be processed and connectors,terminals or adapters may be attached to the components as describedabove.

C. Direct Molding

Alternatively, the panel molding process may be further adapted toencapsulate the PCB panel directly within the mold cavity without usinga center plate (such as center plates 727 in FIGS. 28 and 827 in FIG.37), heat sink panels (such as panels 721, 722 in FIG. 28) or top andbottom plates (such as plates 821, 822 in FIG. 37). In the direct-moldembodiment, the PCB panel may be placed in the bottom mold, with the topmold closing against the bottom (instead of each mold closing againstthe center plate). The depth of the mold cavity may be set to match theoverall height of the PCB panel and components with a custom mold foreach product thickness. Alternatively, the mold cavity may have moveableinterior surfaces that may be adjusted for the selected product orchangeable shim plates designed for each product may be used with astandardized mold to adjust the depth of the mold cavity and thus theencapsulation thickness.

The mold may include fixed or movable registration supports (e.g.similar to registration shelves 828A provided in the center plate 827 inFIG. 37) preferably along the periphery of the mold cavity. The PCBpanel may be seated on the supports to establish the appropriatevertical position in the mold cavity and which may also be used toreduce (displace) the volume of encapsulant in selected regions of thepanel. Referring to FIGS. 43 and 44 for example, an encapsulated PCBpanel 890 produced using the direct mold technique is shown afterremoval from the mold cavity. FIG. 43 shows a bottom view as molded(component top view) of the panel revealing indentations in the curedencapsulant 805, indentations 891 along the sides, indentations 891B atthe corners, a large indentation 891A at one end, and circularindentations 891C and 891D at each end of the panel 890. The largeindentation 891A may be used to expose identifying features on the PCBsuch as a bar code used during manufacture to identify the panel.Similarly, the circular indentations 891C and 891D may be used to exposepositional information on the PCB, such as the fiducial markingsdescribed above.

The PCB panel may be placed in the bottom mold cavity, and the uppermold press may be pressed against the lower mold forming a seal aroundthe cavity. As the upper mold is closed against the lower mold,preferably moveable pins within the upper mold may make contact with thePCB in the regions of the supports to bias the PCB against theregistration supports in the lower mold and securing the PCB panel. Forexample, the top view as molded (component bottom view) of FIG. 44shows, additional circular indentations 891E in the cured encapsulant806 located within the indentations 891 and 891B revealing potentiallocations at which moveable pins may be deployed in the top moldsection. It may be advantageous to locate the movable pins within othersupport features to limit the exposed length of the pin.

With the mold closed and the PCB panel secured, molding compound may beinjected into the mold cavity and cured, e.g. by elevating thetemperature. After the molding compound is cured, the encapsulated PCBpanel may be separated from the upper and lower mold presses, and anyencapsulant remaining on the PCB in the region of holes 891A, 891C, 891Dmay be removed as described above (e.g., by drilling or laser ablation)to expose the identifying features (bar code and fiducial marks) on thePCB panel 124. The PCB panel may be lapped, and singulated as required.

In some implementations, after singulation, a portion of the topencapsulant 822 can be removed by mechanical lapping to expose a topsurface of a magnetic core structure 826. Similarly, a portion of thebottom encapsulant material 824 can be removed by mechanical lapping toexpose a bottom surface of the magnetic core structure 826. The lappingprocess provides great dimensional control of the finished product.

As described above in connection with the heat sink panel versions, thefinished products, e.g. modules made using a standard panel size, mayhave diverse dimensions not only in the lateral (length and width)directions, but also in the vertical (thickness) direction (e.g. due tocomponent thickness). However, because the lateral PCB panel dimensionsremain the same, and variations in component thickness from panel topanel may be accommodated by the molding press, the same general purposemolding equipment may be used for a wide variety of products of diversedimensions to produce a large mix of products.

In some implementations, a panel molding manufacturing process for a mixof products may include some or all of the following steps. Select aspecific product to build. Select the requisite mold presses, e.g. basedupon spacing and height for the specific product. Select the appropriatePCB panel for the specific product. Select and assemble the magneticcores and other components onto the PCB panel, e.g. by surface mountsoldering, etc. Dispense a measured quantity of molding compound intothe bottom mold press. Press the bottom side of PCB panel up againstbottom mold press. Dispense a measured quantity of molding compound onthe top side of the PCB panel. Press top mold press into place on thePCB panel. Inject additional molding compound into the cavity betweenthe top and bottom mold presses and the PCB panel through a channelformed between the top and bottom mold presses. Cure the moldingcompound. Remove the encapsulated PCB panel from the mold presses. Formholes in the encapsulant to expose fiducial marks to facilitatealignment. Cut the encapsulated PCB panel along the cut lines forsingulation. Apply a conformal coating to protect the interconnects, orplate the interconnects, or attach a lead frame, motherboard, orconnector to the exposed interconnects.

In some implementations, a panel molding manufacturing process for a mixof products may include some or all of the following steps. Select aspecific product to build. Select the requisite mold presses, e.g. basedupon spacing and height for the specific product. Select the appropriatePCB panel for the specific product. Select and assemble the magneticcores and other components onto the PCB panel, e.g. by surface mountsoldering, etc. Position the PCB panel in a manifold plate (e.g., 827 inFIGS. 37-42). Press top and bottom mold presses against the manifoldplate. Inject molding compound into the cavity between the top andbottom mold presses and the PCB panel through chambers and channelsformed in the manifold until the PCB panel is entirely enclosed by themolding compound. Cure the molding compound. Remove the manifold plateand the encapsulated PCB panel from the mold presses. Form holes in theencapsulant to expose fiducial marks to facilitate alignment.Mechanically lap one or both surfaces of the panel. Cut the encapsulatedPCB panel along the cut lines for singulation. Apply a conformal coatingto protect the interconnects, or plate the interconnects, or attach alead frame, motherboard, or connector to the exposed interconnects.

IV. Connectors Based on 3D Bar Codes

The 3D bar codes may be used with any of the adapters and connectionmethods described above for the standard, i.e., two-dimensional, barcodes. However, because of the mechanically robust solder jointsattainable using 3D bar codes, additional connection options areavailable with 3D bar codes. Referring to FIG. 47 for example, the 3Dbar code formed in PCB 920, i.e., exposed conductive features 930, maybe surface mount soldered directly to mating contact pads on theexternal circuit board 934. Solder 932 may be applied between theexposed conductive features 930 and the external circuit board 934 toform a metallic bond to the exposed conductive features 930. Because theexposed surface area of the conductive features 930 is increased afterremoving a portion of the insulative material 922, the bonding strengthbetween the solder 932 and the conductive features 930 increases,providing a more robust connection between the PCB panel 920 and theexternal circuit board 934. Although FIGS. 46-47 primarily show the barcode related details of the PCB 920, it should be appreciated that thefigures are representative of a 3D bar code of, and solder connectionsto, a singulated panel molded module, such as, for example, module 940shown in FIG. 48A or 48B.

In general, components having 3D conductive features can be solderattached to metalized substrates. For example, the 3D conductivefeatures can be attached to metalized lead frames using solder paste andstandard SMT reflow profiles for the heat cycle. The 3D conductivefeatures can be attached to the metalized edge of a PCB board. In thisprocess, the surfaces are fluxed and a solder alloy preform is reflowedbetween the substrates. Alternatively, solder paste can be used.

Owing to their increased mechanical robustness, 3D conductive featuresmay be arranged into two or more bar codes in the same space that mightotherwise be provided for a single bar code. Referring to FIG. 48A forexample, two sets of conductive features, 946 and 948 are shown makingup two individual bar code terminals. Because each of the bar codes 946and 948 occupy only a portion of the PCB thickness compared to adjacentbar code 944 which occupies nearly the entire PCB thickness, they appearas “split” bar codes. The split refers to establishing two distinct nodeconnections in the space typically occupied by a single bar code. Inthis example, a panel molded device 940 includes a PCB 942 havingseveral contact sets. For example, a contact set 944 includes a twelveconductive features that together form a single electrical connectionnode. The number and width of the conductive features making up bar code944 may be appropriate for providing a power connection that may be usedto carry relatively large currents. A contact set 946 includes two 3Dconductive features that together form a single electrical connectionnode. A contact set 948 includes two 3D conductive features thattogether form a separate single electrical connection node. The fewerand narrower features in 3D bar codes 946 and 948 may be appropriate forcarrying relatively smaller currents such as for electrical control orstatus signals. In some examples, the contact set 946 and the contactset 948 may be separated by a distance that is at least twice as large,or at least five times as large, as the distance between two adjacentconductive features.

In FIG. 48A, some of the insulation material 922 was masked beforeetching, so portions of the insulation material 922 away from theconductive features 930 remain intact. Referring to FIG. 48B, in someimplementations, the PCB panel 942 is positioned between other modulesthat are covered by encapsulant. In this case, masking may not berequired because the PCB insulation material etches much faster than theencapsulant. The entire edge of the PCB panel 942 is etched, exposingthe 3D conductive features. After etching, the conductive featuresappear to protrude from the edge surface of the insulation material.

A 3D conductive feature has a larger surface area compared to a flat(2D) conductive feature, so when the 3D conductive feature is solderedto a conductive pad of another circuit board, the mechanical strengthprovided by the 3D conductive feature may be significantly greater thanthat provided by a flat conductive feature. As a result, fewer 3Dconductive features may be needed for establishing a reliable connectionfor a single node. Another example of split bar codes includes thecontact sets 950 and 952 each of which includes two relatively wide 3Dconductive features that together provide greater mechanical strengththan the two shorter 3D conductive features of contact set shown for barcodes 946 and 948. In some implementations, each conductive layer in thePCB 942 may vary in thickness from 1.3 mils to 3.3 mils depending on theweight and the manufacturer of the PCB. Each conductive feature in acontact set may not have sufficient conductive surface area to provide amechanically secure solder connection to an external terminal. By usingmultiple conductive features in a contact set and etching the insulationto make 3D conductive features, mechanically robust solder connectionsmay be established.

The distance between the contact sets 946 and 948 in the thicknessdirection may be set to provide adequate clearance between adjacentconductive terminals, e.g., in a 14 layer PCB, conductive layers 2 and 3may form one 3D bar code and conductive layers 14 and 15 may be used toform an adjacent 3D bar code, with conductive layers 4 through 13 beingsetback to provide clearance between the two 3D bar codes as shown inthe example of FIG. 48. Small mid-PCB-elevation bar codes 964 may belocated between the split bar codes as shown in FIGS. 48 and 49. Themid-PCB elevation bar codes may be used during manufacture, e.g., fortesting or programming, rather than for end-user connections to externalcomponents. As shown in FIGS. 49 and 50, the mid-PCB-elevation terminalsmay be left unconnected to a lead frame, and preferably may be coveredwith a non-conductive material such as a structural epoxy.

The 3D bar codes 944, 946, 948, 950, and 952 (FIG. 48) may be solderedto respective conductive pads on another printed circuit board or torespective terminals of a lead frame. Referring to FIG. 49, in someimplementations, conductive terminals or a lead set can be attached tothe 3D bar codes. For example, the panel molded device 940 has split barcodes attached to a lead set 960 for surface mounting to an externalPCB. The leads include small dimples 962 that establish a minimumstandoff distance between the lead and the panel molded component forpreserving a minimum solder thickness for the connection between thetwo. A lead set 970 adapted for through-hole mounting of a 3D split barcoded component to an external PCB is shown in FIG. 50.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, non-metallic mold panels may be used. The center plate may beprovided as a single-use consumable or may be modified to be used as areusable fixture in the molding process. The center plate may beprovided with or without the encapsulation channels. The registrationholes in the heat sink panels may extend completely through the heatsink panels similar to hole 152 shown in FIG. 4B and the registrationpins, e.g. pins 728 (FIGS. 28 and 31), may extend completely througheach of the heat sink panels allowing fasteners to be used inconjunction with the pins to hold the panel assembly together before andafter the encapsulation process. The fasteners may function as or beused in conjunction with a seal around the pin to contain anyencapsulant. Throughput through the mold press may be increased by usingpanel assemblies that are secured together and removed from the moldpress before the panel has cooled or the encapsulant has set or both.The registration pins 728 and corresponding holes 734 may be used toalign the panel assembly during the singulation process. In someexamples, a panel assembly (e.g., 120) may be formed by dispensingencapsulant into a bottom panel mold (e.g., heat sink panel 122),assembling a substrate (e.g., PCB panel 124) into the bottom panel mold,dispensing encapsulant onto a top of the substrate, and assembling a toppanel mold (e.g., heat sink panel 121) onto the substrate. In someexamples, the surfaces of the PCB panel 124 may have conductive featuresthat are covered by an insulative layer. Blank mold panels may bemachined to provide some or all of the various features described abovein an on-demand manufacturing system.

In some examples, the upper and lower heat sinks 121, 122 are clampedtogether by the upper and lower mold presses 161, 162 at respectiveclamp regions of the upper and lower heat sinks 121, 122. The clampregion of the upper heat sink 121 can be located at points along acircumference of an internal cavity defined by the interior surface ofthe upper heat sink 121. The clamp region of the lower heat sink 122 canbe located at points along a circumference of an internal cavity definedby the interior surface of the lower heat sink 122. In some examples,the clamp regions are cut away from the panel assembly 120 to expose theinterconnects 111, 112, and 113. After the cut, portions of the upperand lower heat sinks 121, 122 near an active circuit area remainattached to the panel assembly 120, allowing heat from the activecircuit area during operation to be dissipated through the remainingportions of the upper and lower heat sinks 121, 122. The active circuitarea can be, e.g., an area of the PCB panel 124 having activecomponents, such as magnetic core structures 131 and electroniccomponents 132. Interlocking contours, other than the undercuts 148shown in FIGS. 6, 7, and 12, can also be formed in the interior surfaceof the mold panel, the contour being filled with cured mold compoundenhancing the structural integrity of the singulated module. In someexamples, most of the large-footprint components (e.g., 132-2D, 132-2E,132-2B, 132-2C) are distributed substantially symmetrically betweenquadrants surrounding the transformer core (e.g., 131-2) on a surface ofthe PCB panel 124. For example, in FIG. 27, the input FETs 132-2D and132-2E are distributed substantially symmetrically between theupper-right and lower-right quadrants surrounding the transformer core131-2. The output FETs 132-2B and 132-2C are distributed substantiallysymmetrically between the upper-left and lower-left quadrantssurrounding the transformer core 131-2.

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method of electrically interconnecting circuitassemblies, the method comprising: providing a circuit assembly having atop surface, a bottom surface, and a perimeter edge connecting the topand bottom surfaces, the perimeter edge being formed of insulativematerial and having a plurality of conductive features embedded in thesurface of the perimeter edge, the conductive features each including anexposed edge, the exposed edges being arranged into one or more contactsets, each contact set providing an electrical connection to arespective electrical node of the circuit assembly, comprising one ormore of the conductive features, being separated from adjacent contactsets by a portion of the perimeter edge that is free of conductivefeatures, and being located at an elevation in the perimeter surfacebetween the bottom surface and the top surface; and selectively removingportions of the insulative material from the surface of the perimeteredge adjacent to selected ones of the exposed edges of selected ones ofthe conductive features exposing additional surface area of the selectedones of the conductive features, wherein the additional surface area isrecessed from the perimeter edge and together with the adjacent exposededge forms a three dimensional contact.
 2. The method of claim 1 whereinthe additional surface area forms an angle greater than 45 degrees tothe perimeter edge.
 3. The method of claim 1, further comprisingpreparing the additional surface area of the conductive features forsolder wetting.
 4. The method of claim 1, further comprising applyingsolder paste to the exposed portions of the conductive features.
 5. Themethod of claim 1, further comprising wetting the conductive features inthe recesses and along the perimeter surface with solder.
 6. The methodof claim 1, further comprising placing an external conductive terminaladjacent the conductive features and forming a solder connection betweenthe external conductive terminal and the conductive features.
 7. Themethod of claim 1, further comprising forming a solder connectionbetween each set of the conductive features and a respective conductivepad on a printed circuit board.
 8. The method of claim 1, furthercomprising forming a solder connection between each set of theconductive features and a respective terminal of a lead frame.
 9. Themethod of claim 1 wherein the elevation is approximately midway betweenthe top and bottom surfaces.
 10. The method of claim 1 wherein theselective removing comprises plasma etching.
 11. The method of claim 1wherein the selective removing comprises removing approximately 2.5 to3.5 mils of the insulative material.
 12. The method of claim 1 whereinthe selective removing comprises masking portions of the circuitassembly.
 13. The method of claim 1, comprising forming a plurality ofthree dimensional contacts, arranging the three dimensional contacts ina plurality of contact sets, each contact set having a plurality ofthree dimensional contacts, wherein each contact set is separated fromadjacent contact sets by a portion of the external perimeter edge thatis free of conductive features, and using the plurality of threedimensional contacts of each contact set together to form a distributedelectrical connection to a single electrical node in the circuitassembly.
 14. The method of claim 1 wherein the circuit assemblycomprises a printed circuit board (“PCB”) having a plurality ofconductive layers, the PCB being located at an elevation in theperimeter surface between the first surface and the second surface, atleast one of the first and second surfaces comprise a cured encapsulantmaterial, and the conductive features comprise selected portions of theconductive layers of the PCB.
 15. The method of claim 14 whereinselectively removing portions of material from the perimeter surfacecomprises plasma etching portions of the material in insulation layersin the PCB.
 16. The method of claim 15 wherein selectively removingportions of material from the perimeter surface further comprises mediablasting the plasma etched portions.
 17. The method of claim 16 whereinthe media blasting uses dry ice as a blasting media.
 18. The method ofclaim 10 wherein the selective removing comprises masking portions ofthe circuit assembly.
 19. The method of claim 18 wherein the circuitassembly comprises a printed circuit board (“PCB”) having a plurality ofconductive layers, at least one of the first and second surfacescomprise a cured encapsulant material, and the conductive featurescomprise selected portions of the conductive layers of the PCB.
 20. Themethod of claim 19 wherein selectively removing portions of materialfrom the perimeter surface comprises plasma etching portions of thematerial in insulation layers in the PCB.
 21. The method of claim 20wherein selectively removing portions of material from the perimetersurface further comprises media blasting the plasma etched portions. 22.The method of claim 21 wherein the media blasting uses dry ice as ablasting media.
 23. The method of claim 21, comprising forming aplurality of three dimensional contacts, arranging the three dimensionalcontacts in a plurality of contact sets, each contact set having aplurality of three dimensional contacts, wherein each contact set isseparated from adjacent contact sets by a portion of the externalperimeter edge that is free of conductive features, and using theplurality of three dimensional contacts of each contact set together toform distributed electrical connections to the circuit assembly.
 24. Themethod of claim 21, further comprising preparing the additional surfacearea of the conductive features for solder wetting.
 25. The method ofclaim 23, further comprising applying solder paste to the exposedportions of the conductive features.
 26. The method of claim 21, furthercomprising wetting the conductive features in the recesses and along theperimeter surface with solder.
 27. The method of claim 21, furthercomprising placing an external conductive terminal adjacent theconductive features and forming a solder connection between the externalconductive terminal and the conductive features.
 28. The method of claim21, further comprising forming a solder connection between each set ofthe conductive features and a respective conductive pad on a printedcircuit board.
 29. The method of claim 23, further comprising forming asolder connection between each set of the conductive features and arespective terminal of a lead frame.